1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, it relates to a semiconductor device using a ferroelectric film.
2. Description of the Related Art
In a semiconductor device such as a ferro-electric random access memory (FeRAM) which uses a ferroelectric capacitor employing a ferroelectric film, if hydrogen and/or moisture penetrates the capacitor during, for example, a manufacturing process after the ferroelectric capacitor is formed, characteristics of the ferroelectric capacitor, especially polarization characteristics of the ferroelectric film are deteriorated, resulting in a problem.
A multilevel wiring using a copper wiring and a low dielectric constant insulator is used in a miniaturized ferroelectric random access memory. As the low dielectric constant insulator, there is used, e.g., an organic silicon oxide film (e.g., an SiOC film) or a fluoridated silicon oxide film (e.g., an SiOF film). These films are formed from an organic/inorganic material containing a CH-based or CF-based component as a source material by, e.g., plasma assisted chemical vapor deposition (plasma CVD). Various kinds of radicals such as H or F are generated to a great extent during plasma processing. As the low dielectric constant insulator is porous, the insulator is apt to absorb/adsorb the radicals and moisture as compared to a conventional interlevel insulator, e.g., a TEOS oxide film.
The low dielectric constant insulator even adsorbs hydrogen and/or moisture in a process after its formation. An example of the adsorption is explained below. An upper electrode of a ferroelectric capacitor is connected with a copper wiring through a contact plug provided in the low dielectric constant insulator. The contact plug and the copper wiring are covered with a barrier metal film, e.g., tantalum (Ta) or tantalum nitride (TaN), which prevents copper from diffusing out. Even in a process of forming the barrier metal, the copper wiring or the like, the low dielectric constant insulator is exposed to a processing atmosphere containing hydrogen and/or moisture, thereby absorbing/adsorbing hydrogen and/or moisture.
In order to prevent hydrogen and/or moisture absorbed/adsorbed in the low dielectric constant insulator from penetrating the ferroelectric capacitor, the ferroelectric capacitor is generally covered with a hydrogen barrier film. However, since the contact plug is not covered with the hydrogen barrier film, hydrogen and/or moisture may possibly penetrate into the ferroelectric capacitor through the contact plug.
A semiconductor device comprising a hydrogen barrier film formed in a contact plug portion is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-291843. In the semiconductor device, prior to forming a ferroelectric capacitor, first, nitrogen is plasma-doped on a surface of a first insulator where the ferroelectric capacitor will be formed thereon, thereby forming a first hydrogen barrier film consisting of a nitride of the first insulator. After forming the ferroelectric capacitor, a second insulator is formed over the entire ferroelectric capacitor, and nitrogen is plasma-doped on a surface of the second insulator to form a second hydrogen barrier film consisting of a nitride of the second insulator. Then, a third insulator which functions as an interlevel insulator is formed over the ferroelectric capacitor. A contact hole reaching the ferroelectric capacitor is formed through the third and second insulators, and nitrogen is similarly plasma-doped on an inner surface of the contact hole, thereby forming a third hydrogen barrier film consisting of a nitride of the third insulator.
It is said that a thickness of the hydrogen barrier film formed by plasma doping roughly corresponds to a couple of atomic layers, and thus it is not thick. Therefore, there is a problem of hydrogen barrier properties at a contact portion between the second and third hydrogen barrier film on an inner surface of the contact hole. Further, when a porous low dielectric constant insulator is used as the third insulator, there could be a problem whether the hydrogen barrier film can be sufficiently formed on a porous surface of the low dielectric constant insulator having complicated shapes.